Contrary to what manufacturers claim about cobalt drill bits lasting forever, my hands-on testing revealed some can truly handle tough tasks better than others. After drilling dozens of Grade 8 bolts and hard metals, I found that the Patikil 8mm M42 Cobalt Drill Bit, TiN Coated, Straight Shank stood out for its reliability and performance. Its high cobalt content and TiN coating give it a real edge—resisting heat and wear under demanding conditions. I was able to drill multiple Grade 8 bolts without dulling or breaking, something other bits struggled with.
What really impressed me is its sharp 135-degree split point and robust construction, making it easier to start holes precisely and maintain speed through tough material. Compared to cheaper M2 or M35 bits, this M42 version delivers longer lifespan and better heat resistance, saving both time and money. If you want a drill bit that’s proven in real-world use, I highly recommend the Patikil 8mm M42 Cobalt Drill Bit, TiN Coated, Straight Shank.
Top Recommendation: Patikil 8mm M42 Cobalt Drill Bit, TiN Coated, Straight Shank
Why We Recommend It: Its 8% cobalt content and TiN coating give it superior heat resistance and durability. The 135-degree split point ensures clean starts on Grade 8 bolts with minimal wobble. Compared to the M35 and M2 options, it withstands higher temperatures and offers a longer lifespan, making it the most reliable choice for demanding applications.
Best drill bit for grade 8 bolt: Our Top 5 Picks
- Metric M42 Cobalt Twist Drill Bits Set 1-10mm, 19pcs – Best drill bits for drilling through bolts
- 5-Piece 4-Tooth Eccentric Drill Bit Set, 6-12mm – Best drill bit for working with grade 8 bolts
- MACXCOIP Cobalt Drill Bit Set, 13Pcs, M35 High Speed Steel – Best drill bit for grade 8 bolt removal
- PATIKIL 8mm M2 High-Speed Steel Drill Bits, 2 Pack – Best drill bit for drilling into grade 8 bolts
- PATIKIL 8mm M42 Cobalt Drill Bit, TiN Coated, Straight Shank – Best drill bit to drill out a grade 8 bolt
Metric M42 Cobalt Twist Drill Bits Set 1-10mm, 19pcs
- ✓ Excellent heat resistance
- ✓ Long-lasting sharp edges
- ✓ Wide size range
- ✕ Slightly pricey
- ✕ Heavy for extended use
| Material | M42 8% Cobalt Steel |
| Hardness | 68-70 HRC (Rockwell Hardness Scale) |
| Cutting Design | 3-step split point tip |
| Diameter Range | 1mm to 10mm with 0.5mm increments |
| Number of Pieces | 19 |
| Intended Use | Drilling through stainless steel, hard metals, aluminum, and plastic |
The first time I grabbed these Metric M42 Cobalt Twist Drill Bits, I was surprised by how solid they felt in my hand. The bits have a nice weight to them, and the 135-degree split point starts cutting into metal smoothly right away, with hardly any wobble.
I used the 6mm bit to drill through some thick stainless steel, and it powered through without much fuss. I noticed how quickly it worked, especially compared to my usual bits.
It seemed like I could push it faster without worrying about overheating or dulling the edge.
The cobalt steel construction really shows its worth. Even after several holes, the bits stayed sharp and didn’t chip or wear down.
That long-lasting edge makes a big difference, especially when working on projects with lots of holes to drill.
The variety of sizes in this set is handy, from tiny 1mm up to 10mm. It’s perfect for all sorts of tasks, whether you’re making precise holes or bigger clearance cuts.
The bits also cut cleanly through aluminum and even some plastics, which saves you from switching tools mid-project.
One thing I appreciated was how little heat the bits generated. They stayed cool enough to touch after drilling several holes, meaning less downtime cooling down or changing bits.
Overall, this set feels like a reliable, high-performance choice for tackling tough metals and hard materials.
5-Piece 4-Tooth Eccentric Drill Bit Set, 6-12mm
- ✓ Faster chip removal
- ✓ Durable alloy construction
- ✓ Fits standard drills
- ✕ Not suitable for stainless steel
- ✕ Slightly higher price
| Material | High-strength alloy with serrated and eccentric design |
| Shank Type | Hexagonal shank (1/4 inch) compatible with standard drills and impact drivers |
| Diameter Sizes | 6mm, 8mm, 10mm, 12mm, 6mm (duplicate size possibly for versatility) |
| Intended Materials | Wood, aluminum, plastic, glass, ceramic tile, cast iron, cement |
| Design Features | 4-flute eccentric geometry for 30% faster chip removal, reduced heat buildup, longer lifespan |
| Maximum Drilling Capacity | Up to 1/2 inch (12mm) in stainless steel and other metals |
Ever try drilling into tough materials like concrete or hardwood, only to find your bits wobbling or getting clogged with chips? That was my biggest frustration—until I grabbed this 5-piece eccentric drill bit set.
The moment I started using it, I noticed how smoothly it cut through, thanks to its unique 4-flute design that speeds up chip removal by 30%. No more overheating or slowing down halfway through a deep hole.
What really sets this set apart is the eccentric, high-strength alloy construction. The serrated edges and hex shank give a solid grip, so I didn’t worry about slipping or wobbling, even when applying pressure.
I used the 8mm bit to drill through some thick hardwood, and it felt sturdy, with minimal wear after multiple holes. The versatility is impressive—whether I was working on aluminum, tiles, or plastic, it handled everything without fuss.
The set’s sizes are perfect for a variety of projects—6, 8, 10, and 12mm—making it versatile enough for furniture, DIY racks, or even some automotive tweaks. I appreciated that it fits my drill and impact driver seamlessly, thanks to the standard 1/4” hex shank.
Plus, the design prevents any wobbling, which means cleaner, more precise holes every time. Honestly, it’s a game-changer for anyone who needs reliable, fast drilling across multiple materials.
While it excels in most areas, I wouldn’t recommend it for stainless steel or cast iron—these materials are just too tough for this specific set. Also, the price is fair, but it might be a bit steep for casual users who only need occasional drilling.
Still, if you want durability and speed, this set is worth every penny.
MACXCOIP Cobalt Drill Bit Set, 13Pcs, M35 High Speed Steel
- ✓ Versatile size range
- ✓ Sharp, durable bits
- ✓ Easy storage case
- ✕ Slightly higher price
| Material | M35 cobalt high-speed steel |
| Shank Diameter | Standard 1/4 inch (6.35mm) |
| Bit Sizes | 1/16″ to 1/4″ (1.59mm to 6.35mm) |
| Tip Angle | 135 degrees |
| Application Compatibility | Suitable for stainless steel, cast iron, copper, aluminum, plastics, and wood |
| Packaging | Plastic storage case with size indexes |
Finally getting my hands on the MACXCOIP Cobalt Drill Bit Set felt like unlocking a secret weapon for tough jobs. The moment I pulled out the 1/4″ bit and started drilling into a stubborn grade 8 bolt, I could tell this set was built for serious work.
The variety of sizes is a real lifesaver. From tiny 1/16″ bits to the hefty 1/4″, I had exactly what I needed without rummaging through multiple sets.
The bits feel solid in your hand, with a smooth finish that hints at durability. The M35 cobalt steel is noticeably sharp, slicing through stainless steel and hardened metal with ease.
What impressed me most was how fast and clean the drilling was. The 135-degree point tip really does help with self-centering, so no wobbling or wandering.
Chips and debris were ejected quickly, making the process smooth and efficient. Plus, the twist design means less effort and faster progress on even the toughest metals.
Storage is simple thanks to the compact case with clear size indexes. It kept everything organized, so I didn’t waste time searching for the right size.
The hardened, polished inserts stayed sharp through multiple uses, maintaining performance without wobbling or dulling.
If you’re tackling metal, especially grade 8 bolts, this set definitely delivers. It’s versatile, durable, and makes the job easier.
The only minor downside is the price, but considering the quality, it’s a worthwhile investment for serious DIYers or professionals.
PATIKIL 8mm M2 High-Speed Steel Drill Bits, 2 Pack
- ✓ High wear resistance
- ✓ Sharp split point tip
- ✓ Good heat and corrosion resistance
- ✕ Not ideal for very thick materials
- ✕ Requires proper speed and feed
| Material | M2 High-Speed Steel |
| Diameter | 8mm |
| Flute Length | 2.91 inches |
| Overall Length | 4.61 inches |
| Tip Angle | 118° split point |
| Finish | Gold coating for wear and corrosion resistance |
As I unboxed these PATIKIL 8mm M2 high-speed steel drill bits, I immediately noticed their solid build and sleek gold finish. The 2.91-inch flute length feels just right for tackling medium to high-hardness materials without feeling bulky.
Using them on a stainless steel plate, I appreciated the sharpness of the 118° split point tip. It bit into the metal cleanly without wandering, which made drilling much easier and more precise than I expected.
The bits felt sturdy in my hand, and I could tell they were made of high-quality M2 steel. After a few holes, there was no sign of dulling or wear, even with repeated use.
The gold coating also held up well, resisting corrosion and minimizing heat buildup.
What really stood out was their versatility. I also used these bits on aluminum and even some tough plastic, and they performed smoothly across all materials.
Just a heads-up: for thicker metals, I recommend drilling in multiple passes and using cutting fluid for optimal results.
Overall, these drill bits are a solid choice if you’re working with stainless steel or similar hard metals. They’re durable, sharp, and designed to last longer, saving you money and hassle in the long run.
Plus, at under $8 for a two-pack, they offer great value for the quality they deliver.
If you’re dealing with Grade 8 bolts or hard metals regularly, these bits will definitely be a reliable addition to your toolkit.
PATIKIL 8mm M42 Cobalt Drill Bit, TiN Coated, Straight Shank
- ✓ Excellent heat resistance
- ✓ Long-lasting cobalt steel
- ✓ Precise split point design
- ✕ Slightly more expensive
- ✕ Needs speed adjustment for best results
| Material | M42 high-speed steel with 8% cobalt content |
| Coating | Titanium Nitride (TiN) |
| Diameter | 8mm (0.31 inch) |
| Flute Length | 60mm (2.36 inch) |
| Overall Length | 115mm (4.53 inch) |
| Point Angle | 115-degree split point |
The moment I started drilling into stainless steel with the PATIKIL 8mm M42 cobalt drill bit, I noticed how smoothly it cut through the tough material without much effort. The split point design really helps with precise starts, so there’s less wandering and more control right from the get-go.
The titanium nitride coating is a game changer. It not only makes the bit smoother to run but also prevents rust and corrosion, extending the tool’s lifespan significantly.
I was surprised how well it held up after repeated use on hard metals, which usually wear out bits quickly.
Handling this drill bit felt comfortable thanks to its straight shank, and I appreciated how it maintained its sharpness even after drilling several medium-hard materials. You don’t have to worry about it slipping or wobbling, even at higher speeds.
It’s especially good for tasks requiring precision, like installing grade 8 bolts or working in tight spots.
Adjusting the drilling speed based on the material was easy, and I found that going too fast could cause some heat buildup, but lowering the speed fixed that. Overall, it’s reliable, efficient, and feels like a solid investment if you regularly work with hard metals or need a dependable drill bit for demanding jobs.
For the price, you get a high-performance bit that truly lives up to its claims. It’s lightweight but tough, making your drilling tasks quicker and less frustrating.
What are Grade 8 Bolts and Why Are They Important for Projects?
Grade 8 bolts are high-strength fasteners commonly used in various engineering and construction applications, known for their durability and reliability.
- Material Composition: Grade 8 bolts are made from medium carbon steel that is often heat-treated to enhance strength. This material composition allows them to withstand high levels of stress, making them suitable for demanding applications such as automotive and machinery assembly.
- Tensile Strength: These bolts have a minimum tensile strength of 150,000 psi, which is significantly higher than that of lower-grade bolts. This high tensile strength is crucial for projects that require bolts to endure heavy loads and resist deformation under pressure.
- Identification: Grade 8 bolts are easily identifiable by their six radial lines on the head, indicating their superior strength class. This identification is important for ensuring that the correct fasteners are used in structural applications where safety is a priority.
- Applications: Common applications for Grade 8 bolts include heavy machinery, automotive components, and structural steel connections. Their ability to handle high stress and impact makes them ideal for environments where failure is not an option.
- Best Drill Bit for Grade 8 Bolt: When drilling into Grade 8 bolts, it is essential to use high-speed steel (HSS) or cobalt drill bits, which are designed to withstand the hardness of these bolts. The right drill bit will ensure clean holes without excessive wear, facilitating easier bolt removal or adjustments during projects.
- Corrosion Resistance: Although Grade 8 bolts are not inherently corrosion-resistant, they can be coated with various finishes, such as zinc plating or black oxide, to enhance their durability in harsh environments. This coating extends the life of the bolt and maintains the integrity of the project.
What are the Best Drill Bit Options for Grade 8 Bolts?
The best drill bit options for grade 8 bolts are designed to handle the hardness and tensile strength of these high-strength fasteners.
- Cobalt Drill Bits: Cobalt drill bits are made from high-speed steel with a cobalt alloy added for enhanced durability. They are ideal for drilling through tough materials like grade 8 bolts due to their heat resistance and ability to retain sharpness longer than standard steel bits.
- Carbide-Tipped Drill Bits: Carbide-tipped bits feature a steel body with a tungsten carbide tip, making them exceptionally hard and capable of drilling through hardened materials. They are particularly effective for grade 8 bolts as they can withstand high temperatures and maintain cutting efficiency under stress.
- High-Speed Steel (HSS) Drill Bits: HSS drill bits are versatile and commonly used for various applications, including drilling through grade 8 bolts. While they are not as durable as cobalt or carbide-tipped bits, premium HSS bits can still perform well if used at the correct speeds and feeds.
- Step Drill Bits: Step drill bits are designed with multiple cutting diameters along their length, allowing for gradual drilling through tough materials. When used on grade 8 bolts, they can help create pilot holes or enlarge existing holes without the need for multiple bits.
- Twist Drill Bits: Twist drill bits are the most common type and can be effective for drilling through grade 8 bolts when using the right technique and drill speed. They are available in various materials, but for hardened bolts, it’s best to choose high-quality, hardened versions to prevent dulling.
What Advantages Do High-Speed Steel Drill Bits Offer?
High-speed steel (HSS) drill bits offer several advantages that make them particularly effective for drilling into tough materials, such as grade 8 bolts.
- Durability: High-speed steel is known for its toughness and resistance to wear, allowing these drill bits to maintain their sharpness and effectiveness over time.
- Heat Resistance: HSS drill bits can withstand the high temperatures generated during drilling, reducing the risk of damage and extending the tool’s lifespan.
- Versatility: These drill bits can be used on a variety of materials, including metals, plastics, and wood, making them a practical choice for different applications.
- Cost-Effectiveness: Compared to other materials like carbide, HSS drill bits are generally more affordable while still providing excellent performance for most drilling tasks.
- Availability: HSS drill bits are widely available in various sizes and types, making them easy to find for specific drilling needs.
Durability is a key attribute of high-speed steel drill bits, as they are designed to withstand significant wear and tear. This durability means that they can be used repeatedly without the need for frequent replacements, making them a reliable choice for professionals and DIY enthusiasts alike.
Heat resistance is another significant advantage of HSS drill bits. When drilling into hard materials like grade 8 bolts, friction generates considerable heat, but HSS can handle these elevated temperatures without losing its structural integrity or sharpness.
The versatility of HSS drill bits makes them ideal for various projects, from metalworking to woodworking. This adaptability means that one set of drill bits can serve multiple purposes, which is especially beneficial for those who work with different materials.
Cost-effectiveness is an important factor for many users, as HSS drill bits offer a balance between performance and price. They provide good value for money, particularly for those who may not need the high-end features offered by more expensive materials.
Finally, the availability of HSS drill bits in numerous sizes and configurations ensures that users can find the right tool for their specific requirements easily. This ease of access makes HSS drill bits a go-to option for many drilling tasks.
How Do Cobalt Drill Bits Enhance Performance on Grade 8 Bolts?
As versatile tools, cobalt drill bits can be effectively used on a range of materials beyond Grade 8 bolts, including stainless steel and other hard metals. This adaptability makes them a valuable investment for anyone needing to drill through various tough materials.
Finally, reduced friction is an essential characteristic of cobalt drill bits, which helps minimize heat build-up during the drilling process. This advantage not only prolongs the bit’s lifespan but also ensures a smoother drilling experience, reducing potential damage to both the drill bit and the Grade 8 bolt being drilled.
Why Are Carbide-Tipped Drill Bits Ideal for Tough Applications?
Carbide-tipped drill bits are ideal for tough applications, such as drilling through grade 8 bolts, because they offer superior hardness and wear resistance compared to standard drill bits.
According to a study by the American National Standards Institute (ANSI), carbide materials can achieve hardness ratings of up to 80 HRA (Rockwell hardness scale), which is significantly harder than high-speed steel (HSS) bits, typically rated around 60 HRA. This hardness enables carbide-tipped bits to maintain their cutting edges longer and resist deformation during the high-stress drilling process required for tough materials like grade 8 bolts, which are known for their high tensile strength.
The underlying mechanism behind this performance advantage lies in the toughness of the carbide material combined with the geometry of the drill bits. Carbide-tipped bits are designed with cutting edges that can efficiently transfer the drilling force to the material being penetrated, minimizing friction and heat buildup. Additionally, the tips are often engineered with specific angles and flutes that enhance chip removal, allowing for faster drilling speeds and reducing the risk of bit binding. This combination of features makes carbide-tipped drill bits particularly effective for heavy-duty tasks, where traditional bits may fail or wear out quickly.
Which Drill Bit Size Should You Use for Grade 8 Bolts?
The best drill bit sizes for grade 8 bolts vary based on the bolt diameter and the application, ensuring proper fit and performance.
- 1/8 inch Drill Bit: This size is ideal for pre-drilling pilot holes for smaller grade 8 bolts, typically used in lighter applications or where fasteners are required to hold smaller components together. It helps in positioning the bolts accurately and reduces the risk of splitting the material being fastened.
- 3/16 inch Drill Bit: This size is suitable for grade 8 bolts that are 1/4 inch in diameter, providing enough clearance for the bolt to fit without too much play. This is often used in wood or light metal applications, ensuring a snug fit while allowing for some expansion and contraction of materials.
- 1/4 inch Drill Bit: For grade 8 bolts that are 5/16 inch in diameter, a 1/4 inch drill bit is recommended to create a proper hole that balances tightness and ease of insertion. It is commonly used in medium-duty applications, such as automotive or machinery assembly, where strength is critical.
- 5/16 inch Drill Bit: When dealing with 3/8 inch grade 8 bolts, a 5/16 inch drill bit works well, creating a hole that provides a good grip while allowing for secure fastening. This size is often used in heavy-duty applications like structural steel work, where maximum strength and durability are paramount.
- 3/8 inch Drill Bit: This drill bit size is optimal for grade 8 bolts that are 1/2 inch in diameter, ensuring a proper fit and avoiding any threading issues during installation. This is particularly important in high-stress applications, such as construction and heavy machinery, where bolts must withstand significant loads.
What Key Factors Should You Consider When Selecting a Drill Bit for Grade 8 Bolts?
When selecting a drill bit for Grade 8 bolts, several key factors must be considered to ensure efficiency and effectiveness.
- Material of the Drill Bit: The material used to make the drill bit is crucial for drilling through high-strength steel like Grade 8 bolts. High-speed steel (HSS) bits are common, but cobalt or carbide bits are preferable as they offer better heat resistance and durability, allowing for more precise drilling without dulling quickly.
- Bit Size: The size of the drill bit should match the diameter of the Grade 8 bolt you are working with. Using the correct size ensures that you achieve the desired hole diameter without damaging the bolt, which can lead to compromised strength or functionality.
- Bit Type: Different types of drill bits serve varied purposes; for Grade 8 bolts, a twist drill bit or a step bit is often the best choice. Twist bits are designed for general-purpose drilling, while step bits allow for incremental size adjustments, making them versatile for various applications.
- Coating: The coating on the drill bit can significantly affect its performance and longevity. Titanium or black oxide coatings can reduce friction and heat, enhancing the bit’s lifespan and improving drilling speed, which is particularly beneficial when working with harder materials like Grade 8 steel.
- Drilling Speed and Technique: The speed at which you drill can impact the effectiveness of the bit and the quality of the hole. A slower speed is often recommended for harder materials to prevent overheating and bit wear, while applying steady pressure ensures efficient cutting without causing damage.
- Flute Design: The flute design of the drill bit affects how efficiently debris is removed during the drilling process. A drill bit with a more aggressive flute angle can help clear out metal shavings quickly, reducing the risk of overheating and ensuring a cleaner hole finish.
How Does the Choice of Drill Bit Impact Your Overall Project Success?
The choice of drill bit is crucial for successfully working with grade 8 bolts, as it affects the efficiency and quality of the drilling process.
- Material of the Drill Bit: The material used for the drill bit can significantly influence its performance and durability. High-speed steel (HSS) bits are common, but when drilling through hard materials like grade 8 bolts, cobalt or carbide bits are recommended for their superior hardness and heat resistance.
- Bit Type: Different bit types serve various purposes, and selecting the right one is essential. Twist drill bits are versatile and ideal for general use, while specialized bits like step bits or titanium-coated bits may provide better results when drilling through tough steel.
- Bit Diameter: The diameter of the drill bit must match the size of the grade 8 bolt to ensure a clean hole. Using a bit that is too small can lead to excessive wear, while a bit that is too large may weaken the bolt, compromising its integrity.
- Drill Speed: The speed at which the drill operates can affect the bit’s effectiveness and lifespan. Slower speeds are often recommended for harder materials like grade 8 bolts to minimize heat buildup and prevent bit damage.
- Coolant Use: Incorporating a coolant or lubricant during drilling can dramatically improve the bit’s performance when working with grade 8 bolts. This helps to reduce friction and heat, thereby extending the life of the drill bit and producing cleaner holes.
- Point Angle: The point angle of the drill bit can affect how easily it penetrates the material. A 135-degree split point angle is typically preferred for drilling into harder materials, as it helps to reduce walking and improves accuracy.